Embodiments relate to an image sensor having a micro-lens array and a method for fabricating the same. Embodiments may also relate to an image senor that may have a micro-lens array formed by using dry film resist and a method for fabricating the same.
An image sensor may be a semiconductor device for converting optical images into electric signals, and may mainly be classified as either a charge coupled device (CCD) image sensor or a complementary metal oxide semiconductor (CMOS) image sensor.
Various technologies have been developed for fabricating an image sensor to more precisely detect a quantity of light supplied from an exterior.
For instance, a CMOS image sensor may include a photo detector for detecting light and a logic circuit for converting detected light into electric signals that may represent the light is data. The photo detector may include a photodiode which may be formed by implanting low-density conductive impurities a semiconductor substrate.
When fabricating a CMOS image sensor including the photo detector and the logic circuit, a fill factor, which is a ratio of a photo detector area to the whole area of the image sensor, may be increased, which may improve a photo sensitivity of the image sensor.
However, since a photo detector may be formed on a specific area of a CMOS image sensor other than the logic circuit, it may be difficult to enlarge the photo detector area.
For this reason, various photo-gathering technologies have been studied with respect to changing a path of light incident to an area other than the photo detector area such that the light may be gathered in the photo detector. For example, a micro-lens array may be formed on a top surface of a color filter array of an image sensor to guide the light incident to an area other than the photo detector area toward the photo detector.
To fabricate a micro-lens array of an image sensor according to related art, a liquid-phase photoresist may be spin-coated on a color filter of the image sensor. A baking process may then be performed.
An exposure process may be performed, for example using defocus phenomenon. The photoresist may thereby be patterned in a form of a trapezoidal shape. Then, the photoresist pattern having the trapezoidal shape may be melted, for example by applying heat to the photoresist pattern up to a melting point, thereby reflowing the photoresist pattern.
The photoresist pattern that has been subjected to the reflow process may have a convex spherical shape. Then, the photoresist pattern having the convex spherical shape may be cured through a curing process to form the micro-lens array.
However, a process time of about 300 seconds per wafer may be required for reflowing and curing the photoresist pattern. Accordingly productivity of image sensor fabrication may be lowered.
In addition, in a micro-lens array obtained through the reflow process, it may be difficult to uniformly form the curvature of all lenses. Accordingly a performance of the micro-lens array may be degraded.